The invention relates to a phantom system for the calibration and/or characterization of an imaging configuration, as well as a use of the phantom system, and an imaging configuration with this phantom system.
A phantom for MRI, PET, and X-ray configurations is known, for example, from U.S. Pat. No. 7,056,019 B1.
Phantoms are established tools for the characterization and/or calibration of imaging systems with respect to spatial resolution, sensitivity, or geometrical distortion. For MPI (magnetic particle imaging) applications, in particular, the availability of standard phantoms is particularly desirable in order to simplify direct comparison among the various MPI scanner designs, which have been developed since this new imaging method has become established. Critical parameters for characterizing MPI systems are (anisotropic) spatial resolution, geometrical accuracy of the image, signal homogeneity across the image volume, and sensitivity. In order to glean valuable information about the practical use of the systems, these parameters must be tested with the same (usually liquid) contrast media, which are also used in subsequent experiments, as these can also influence those parameters, in particular, spatial resolution and sensitivity.
Until now, mainly ad hoc or makeshift phantoms were used in MPI development. One typical technology is the use of thin tubes that are filled with contrast medium and then bent into a desired spatial shape (Konkle, J. et al “Projection Reconstruction Magnetic Particle Imaging” IEEE Trans Med imaging, 2013 Feb.; 32(2); 338-347.). Other groups use conventional test vessels, which are molded into a defined spatial configuration using adhesive tape or foam-rubber matrix structures. Polyacrylic flow phantoms have also been used, through whose channels liquid containing contrast medium can be pumped. The disadvantage of ad-hoc solutions is the lack of reproducibility and transferability. The use of filled tubes restricts the design of the phantom because spatial path patterns always occur. What is more, air bubbles in the tube are difficult to eliminate. Phantoms based on polyacrylic, in particular, have the disadvantage that small volumes of aqueous contrast medium can dry up due to the absorption of water by the matrix. With such phantom configurations, it is therefore not possible to introduce liquid contrast medium into the imaging system in a well-defined spatial configuration.
Because the MPI method typically requires a second measuring method to provide a morphological reference, it is desirable to use such phantoms that also provide a good contrast in other methods such as MRI or μCT. However, the contrast media used for MPI generate black images with conventional MRI measuring sequences. With existing MPI phantom concepts, it is very difficult to place MRI-active and MPI-active image elements into a well-defined mutual spatial relationship.
U.S. Pat. No. 7,056,019 B1 discloses a phantom system for the calibration of various imaging methods, such as, for example, CT, PET, or MRI scanners. This phantom system comprises a transparent cubic housing with a central opening, in which a measuring head can be inserted. A multiplicity of small holes is provided in the housing. Different cylindrical probes can be inserted into these holes, which, due to their density, can simulate different tissue types. However, liquid contrast media cannot be used with this phantom system. The phantom system known from U.S. Pat. No. 7,056,019 B1 is therefore only of limited suitability for MPI measurements.
The object of this invention is to provide a phantom system, which, in particular with liquid contrast media, permits good contrast with various methods such as MPI, MRI, or μCT (multi-modal). Because the spatial resolution of the MPI scanner is typically anisotropic, it is furthermore desirable to permit different phantom orientations.